In the field of radio communication, one of the core techniques in a physical layer of a communication network is a multiple access (MA) technique, which defines a fashion for simultaneous communication between multiple users. Each of the users will occupy a certain time-frequency resource in communication. According to different resource allocation fashions, the MA techniques may be classified into an orthogonal MA (OMA) technique and a non-orthogonal MA (NOMA) technique. In a certain multiple user communication system, if the time-frequency resources occupied by any two of the users are not overlapped, it is considered that the communication system uses the OMA technique. Otherwise, it is considered that the communication system uses the NOMA technique. For example, in a first generation mobile communication system, a frequency division MA (FDMA) technique is mainly adopted. That is, an available frequency band may be divided into several sub-frequency bands which are not mutually overlapped, and in communication, different sub-frequency bands may be allocated to different user for occupation. Thus, from the point of the division of the time-frequency resource, the resources occupied by any two users in FDMA are not overlapped mutually, which is a typical OMA technique. Other typical OMA techniques include a time division MA (TDMA) technique and a orthogonal FDMA (OFDMA) technique.
Interleaving is an operation for a vector, that is, an operation to rearrange elements in the vector in a certain rule to obtain a new vector with an unchanged length. De-interleaving is an inverse process of the interleaving. An interleaver is a module to carry out the interleaving operation, an input and an output of which are vectors with equal lengths.
At first, the interleaving is used in channel coding and decoding. Generally, for a string of coded bits with errors, if these errors are dispersed discretely, these errors may be corrected by using an error correcting code with a larger probability, and if there errors are dispersed continuously, the error correcting performance will be decreased significantly when using the error correcting code. Therefore, at a transmitting end, the coded bits may be interleaved, and when passing through the channel, errors may be generated on certain several continuous bits. At a receiving end, after de-interleaving, these continuous errors are dispersed, thereby facilitating channel decoding. In the channel coding and decoding, interleavers used by different users are generally completely the same. Then, it is discovered by the researcher that, if different users use different interleavers, signals from different users may be correctly detected at the receiving end by designing carefully a detection algorithm at the receiving end. Thus, an interleave division MA (IDMA) techniques is formed, which has a general structure as follows: signals from each user are coded in a lower speed, generally using repetition coding (which may also be referred to as spreading in this case), and then an interleaver is provided, which is different from those of other users.
In IDMA, all users occupy all of the time-frequency resources which are completely overlapped. IDMA is a typical prospective NOMA technique. As compared with other MA techniques, such as frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA), IDMA has advantages of high power efficiency and low decoding complexity, and is expected to be applied in a next generation of radio communication system. The high power efficiency of IDMA is determined by its non-orthogonality, and is achieved by a user-wise power allocation. The low decoding complexity of IDMA is ensured by slice-wise detection algorithm adopted by the receiving terminal. To further reduce the complexity and compensate for channel fading, the orthogonal frequency division multiplexing (OFDM) technique and the interleave division multiple access (IDMA) technique may be combined, to form an OFDM-IDMA communication system, which has the advantages of the OFMD system and the IDMA system, and thus becomes a better candidate multiple access solution for the next generation mobile communication system.
However, it has become a new challenge for those skilled in the art how to further improve transmission performance of the NOMA communication system.